1. Field of the Invention
The present invention generally relates to fiber optic sensors and, more particularly, to temperature compensation of fiber optic sensors employing self-assembled thin films.
2. Description of the Prior Art
There has been much recent interest in fiber-optic devices using so-called self-assembled multi-layer thin films. These sensors using self-assembled multi-layer thin films function by reflecting or scattering light to the cladding which is formed of the self-assembled thin films (which are easily and rapidly formed with excellent uniformity and repeatability by alternate immersion in any of a wide variety of cationic and anionic solutions at room temperature) and sensing is accomplished by detection of change in transmitted or reflected light due to changes in the optical thickness of a coating such as cladding. (Optical thickness is a function of actual or physical thickness; differing therefrom by a factor which is the index of refraction of the material.) Therefore, such sensors are particularly well-adapted to detection of the presence of chemical and biological materials in the environment of the sensor which may be absorbed, adsorbed or otherwise bound, possibly selectively, to or in the coating which thus changes the physical and/or optical thickness of the coating, leading to many potential applications in medicine, biotechnology and national security for detection of, for example, DNA hybridization or bacteria detection or even for the study of self-assembled thin-films themselves and their formation. Such sensing and/or measurement using sensors including self-assembled multi-layer thin films is more rapid than other material detection techniques and the signals produced by such sensors are stable with high visibility. By the same token, however, these mechanisms providing high sensitivity to the optical thickness of thin films (which also makes such sensors useful for the study of the thin films themselves) also provide high sensitivity to temperature changes which may be useful for temperature measurements but may be a source of error for other parameters of interest such as the presence of particular materials. The existence of such a potential source of error compromises both sensitivity and specificity of the sensor and, indeed, it has been necessary in some applications to increase the concentration of a material for it to be reliably detected.
Within the area of biological material detectors, it is known to use labels (e.g. fluorescence) for particular materials. However, the use of such labels may interfere with a process being monitored, such as the evolution of a material during a chemical reaction, in ways which may not be predictable and, in any event, detection of a label, at best, provides only an indirect measurement of the parameter of interest. Therefore, there is interest in developing sensors for chemical and biological materials which do not require use of a label, referred to as label-free detection.